Conventionally, in order to realize a structure which is folded and implemented in various electric/electronic devices (flex-to-install structure), various wiring boards have been used, such as a flexible wiring board which has flexibility, a joint wiring board obtained by joining a rigid wiring board which is relatively hard and does not have flexibility with the relevant flexible wiring board, or a rigid-flexible wiring board obtained by integrating the relevant flexible wiring board and the relevant rigid wiring board without forming a junction therebetween.
In particular, as wiring boards for limited usage of folding, a wiring board is known which is obtained by performing spot facing processing on a rigid wiring board with a machining tool such as an endmill, and thereby, can be folded at an opening part formed by the relevant spot facing processing as a folding point. Adopting such a structure enables costs to be reduced to the wiring board. For example, as the rigid wiring board which undergoes the spot facing processing, a prepreg is used which is a base material in the state where one glass cloth is immersed in thermosetting resin such as epoxy resin, and after that, it is dried under heating and is semi-set. Moreover, Patent Literatures 1 and 2 disclose printed circuit boards employing such a foldable structure.